U.S. patent number 4,713,765 [Application Number 06/704,032] was granted by the patent office on 1987-12-15 for control system for an engine having an air intake passage.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Tomoaki Abe, Susumu Akiyama, Hideya Fujisawa, Katsunori Ito, Masumi Kinugawa, Tiaki Mizuno, Norio Omori, Toshitaka Yamada.
United States Patent |
4,713,765 |
Abe , et al. |
December 15, 1987 |
Control system for an engine having an air intake passage
Abstract
A control system for an engine has a temperature sensitive
element as part of a device for measuring the air flow in an air
intake manifold to the engine. Further, a first pulse signal is
generated, corresponding to the rotation of the engine, for
controlling the setting of a flip-flop. A transistor is conducted
in the set state of the flip-flop to supply a heating electric
current to the element. The element supplied with the current is
raised to the temperature that corresponds to the air flow in the
manifold. When the temperature of the element is raised until the
specified temperature difference to the air temperature (measured
by a sub temperature sensitive element) is set, the temperature
difference is detected by a comparator, and the flip-flop is reset
by the detection signal. A pulse-shaped signal corresponding to the
set state of the flip-flop is produced as a measurement output
signal, supplied as one detection signal of the operating state of
the engine to an engine control unit, and the current to the
element is controlled to be supplied by the pulse-shaped
signal.
Inventors: |
Abe; Tomoaki (Nagoya,
JP), Fujisawa; Hideya (Kariya, JP), Omori;
Norio (Kariya, JP), Kinugawa; Masumi (Okazaki,
JP), Ito; Katsunori (Aichi, JP), Akiyama;
Susumu (Kariya, JP), Mizuno; Tiaki (Toyota,
JP), Yamada; Toshitaka (Nagoya, JP) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JP)
|
Family
ID: |
27521538 |
Appl.
No.: |
06/704,032 |
Filed: |
February 21, 1985 |
Foreign Application Priority Data
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Feb 24, 1984 [JP] |
|
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59-33595 |
Mar 7, 1984 [JP] |
|
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59-43701 |
Mar 7, 1984 [JP] |
|
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59-43702 |
Apr 11, 1984 [JP] |
|
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59-72188 |
Apr 16, 1984 [JP] |
|
|
59-76267 |
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Current U.S.
Class: |
701/103; 123/494;
700/282; 702/130; 702/46; 73/114.34 |
Current CPC
Class: |
F02D
41/187 (20130101) |
Current International
Class: |
F02D
41/18 (20060101); F02M 051/00 (); G01F
001/68 () |
Field of
Search: |
;364/431.05,510 ;123/494
;73/204,118.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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51-64134 |
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Jun 1976 |
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JP |
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55-57112 |
|
Apr 1980 |
|
JP |
|
55-104538 |
|
Aug 1980 |
|
JP |
|
56-24521 |
|
Mar 1981 |
|
JP |
|
0884462 |
|
Dec 1961 |
|
GB |
|
Primary Examiner: Lall; Parshotam S.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A control system for an engine having an air intake passage,
comprising:
means for generating a first pulse signal at every predetermined
angular rotation of said engine;
means disposed in said air intake passage for generating heat in
accordance with an electric current supplied thereto and for
measuring the temperature of itself;
means for detecting the temperature of air passing through said air
intake passage;
means for establishing a reference temperature in accordance with
the air temperature detected by said air temperature detecting
means;
means for comparing the temperature of said heat generating means
with the reference temperature established by said reference
establishing means, said comparing means generating an output
signal when the temperature of said heat generating means is higher
than the reference temperature;
means for generating a second pulse signal having a period starting
from the first pulse signal and ending with an output of said
comparing means indicating that the temperature of said heat
generating means attains the reference temperature, the period of
said second pulse signal being indicative of an amount of air
sucked into said engine per the predetermined angular rotation of
said engine;
means for supplying said heat generating means with the electric
current during the period of said second pulse signal so that said
heat generating means generates heat during said second pulse
signal and dissipates heat thereafter; and
means for supplying said engine with fuel in accordance with the
period of said second pulse signal.
2. A control system according to claim 1, wherein said electric
current supplying means includes:
a voltage source;
a reference voltage circuit for producing a predetermined reference
voltage;
a transistor having a base connected to said second pulse signal
generating means and an emitter-collector path connected in series
with said voltage source and said heat generating means, said
transistor being turned on in response to said second pulse signal
to supply said heat generating means with a voltage from said
voltage source; and
a comparator connected to receive the voltage supplied to said heat
generating means and the predetermined reference voltage of said
reference voltage circuit, said comparator being further connected
to the base of said transistor to control the turning on and off of
said transistor in response to an output signal of said comparator
so that the voltage supplied to said heat generating means is kept
constant.
3. A control system according to claim 1 further comprising:
a reference voltage circuit for producing a predetermined reference
voltage;
a resistor connected between said heat generating means and said
comparing means; and
a constant current circuit connected in parallel with said heat
generating means and said resistor, and responsive to the reference
voltage of said reference voltage circuit for regulating an
electric current flowing through said resistor at a value
proportional to the reference voltage, and wherein said current
supplying means includes a constant voltage circuit connected to
said reference voltage circuit for supplying said heat generating
means with a constant voltage proportional to said reference
voltage in response to the second pulse signal.
4. A control system according to claim 1, wherein said first pulse
signal generating means includes:
a rotation detector for generating a rotation pulse at every
predetermined angular rotation of said engine;
means for discriminating whether the rotational speed of said
engine is above or belcw a predetermined speed, said discriminating
means generating a first and second signal indicating that the
rotational speed of said engine is below or above the predetermined
speed, respectively;
means for dividing said rotation pulse into different frequencies
in response to said second output signal of said discriminating
means; and
means for selecting either the rotation pulse or the
frequency-divided rotation pulse as said first pulse signal in
response to the first and second output signals of said
discriminating means.
5. A control system according to claim 4, wherein the predetermined
speed of said discriminating means is set to different values when
the number of rotations of the engine is varied to rise and fall in
such a manner that the predetermined speed when the number of
rotations of the engine rises is set to a speed higher than the
predetermined speed when the number of rotations of the engine
falls.
6. A control system according to claim 1, wherein the first pulse
signal generated from said first pulse signal generating means and
the second pulse signal generated from said second pulse signal
generating means are transmitted to and from said second pulse
signal generating means, respectively, through a common signal
line.
7. A control system according to claim 1, wherein said second pulse
generating means includes means for preventing the inverting
operation due to the output signal from said comparing means at a
time interval specified once the said first pulse signal is
raised.
8. A control system according to claim 7, wherein said second pulse
generating means is set to the first state by said first pulse
signal, and composed of a flip-flop inverted by the output signal
from said comparing means to the second state, and said flip-flop
is composed as a level trigger type so that said first state is
maintained even if the output signal is generated from said
comparing means in the state that said first pulse signal is
presented.
9. A control system according to claim 8, wherein the length of
said first pulse signal is set to the length of time specified to
execute the prevention of the inversion of said second pulse
generating means.
10. A control system according to claim 7, wherein means for
preventing said inverting operation is composed of a switch circuit
interposed between said comparing means and said second pulse
generating means, and said switch circuit is set to open the length
of time specified from the rising edge of said first pulse
signal.
11. A control system for an engine having an air intake passage,
comprising:
first resistance means, including a first resistor whose resistance
value varies in accordance with the temperature of air passing
through said air intake passage, for generating a first output
signal corresponding to the resistance value of said first
resistor;
second resistance means, including a second resistor positioned in
said air intake passage and having a resistance value that varies
in accordance with the temperature thereof, for generating a second
output signal corresponding to the resistance value of said second
resistor;
comparator means, connected to said first resistance means and said
second resistance means, for comparing said second output signal
with said first output signal to generate a third output signal
when said second output signal reaches a level of said first output
signal;
rotation detector means for generating a fourth output signal
synchronously with the predetermined angular rotation of said
engine;
pulse generating means for generating a fifth output pulse signal
having a time width starting from said fourth output signal and
ending with said third output signal, said fifth output signal
being indicative of amount of air in said air intake passage per a
predetermined rotation;
power control means for controlling a supply of electrical power to
said second resistance means in response to said fifth output pulse
signal so that said second resistor generates heat during the time
width of said fifth output pulse signal and dissipates the heat
after said fifth output pulse signal; and
fuel control means for controlling the amount of fuel supply in
accordance with the time width of said fifth output pulse
signal.
12. A control system for an engine having an air intake passage
comprising:
an electric power source;
a heater resistor positioned in said intake air passage for
generating heat when an electric current is supplied from said
power source, the resistance value of said heater resistor varying
in accordance with the temperature thereof;
a first resistor connected in series with said heater resistor;
a sensing resistor positioned upstream said heater resistor in said
intake air passage for sensing the temperature of air passing
therethrough, the resistance value of said sensing resistor varying
in accordance with the sensed air temperature;
a second resistor connected in series with said sensing
resistor;
a comparator connected to a first junction between said heater
resistor and said first resistor and a second junction between said
sensing resistor and said second resistor, said comparator
producing an output signal when a first signal developed at said
first juntion reaches the level of a second signal developed at
said second junction;
a rotation detector for generating a rotation pulse synchronously
with the predetermined angular rotation of said engine;
switching means for switching on and off an electrical connection
between said power source and said heater resistor in response to
the rotation pulse of said rotation detector and said output signal
of said comparator, respectively;
measuring means for measuring an interval of time from the rotation
pulse to the output signal from said comparator; and
fuel supply means for supplying said engine with fuel during an
interval of time proportional to a measured interval of time.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a control system for an engine
having an air intake passage, and more particularly to an
improvement in the detecting means for detecting the amount of air
sucked into the engine. This is used as one of the means for
detecting the operating state of an engine so as to obtain a more
accurate air flow rate measurement signal, thereby controlling the
operation of the engine more accurately.
When an engine is electronically controlled, it is necessary to
always monitor its operating state. Monitoring means of the
operating state, rotating speed detecting means, engine temperature
detecting means, exhaust gas temperature detecting means, and
throttle opening detecting means of the engine are presented, and
as a direct relation to the operating state, measuring means of the
air intake flow to the engine is presented.
As measurement detecting means of the air intake flow (used as an
operating state detecting means of this engine), a heat type air
flow sensor, for example, is used. This sensor is disposed in the
intake manifold for supplying combustion air to the engine, has a
heater controlled for heating, and is constructed to detect and
measure the temperature changes of the heater.
The heater is set so that it is exposed to the air flow in the
intake manifold, and the heat dissipating effect is variably
controlled by the air flow. Therefore, the temperature of the
heater corresponds to the air flow velocity in the intake tube, and
the air flow in the intake manifold can be noted by monitoring the
varying temperature of the heater.
More particularly, the heater constitutes a temperature sensitive
element in which its resistance value varies in accordance with the
temperature, and the element is constructed to control the heating
electric current controlled in an analog manner with a constant
temperature. In this case, since a heat dissipating effect
corresponding to the air flow in the manifold is set by the
element, the amount of electric current used for heating (heating
electric current) increases so as to hold the temperature of the
element constant when the air flow is increased. More specifically,
the temperature state of the element is detected from the
resistance value of the element, the amount of heating electric
current to the element is controlled so that the temperature is
maintained at a specified value, and the amount of air flowing in
the manifold is calculated from the amount of the heating electric
current.
However, in such an air flow measuring means, the temperature
sensitive element set in an air flow to be measured is constructed
to control an electric current controlled in an analog manner in a
constant temperature state. When the air flow is, for example,
varied 100 times, the heating, electric current value to the
element varies approximately twice. Therefore, it is necessary to
set offset processing means in a measurement output signal
amplifier circuit to employ the measuring means for controlling an
engine, and the control circuit thereof becomes complicated.
Further, when an engine is controlled by a microcomputer, it is
necessary to convert an analog signal, corresponding to a heating
current value from a sensor, into digital data and to supply it to
an engine control circuit. Consequently, when the measuring means
for obtaining the measurement output signal of such an analog state
is employed, a highly accurate A/D converting operation must be
executed, and an extremely accurate reference voltage power source
for the A/D converter is required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control
system, for an engine having an air intake passage, which can
measure the intake air flow supplied to the engine when it is
operating, which can measure the air flow with sensitivity but with
a simple construction, and which has an intake manifold to
effectively control the engine by such means as the control of the
fuel injection system.
It is another object of the present invention to provide a control
system, for an engine having an air intake passage, which can
execute the measuring operation of the air intake flow so that it
corresponds to the speed of the engine, calculate and output, for
example, the amount of fuel needed to operate the engine, and
execute the control of the engine in correspondence with the speed
of the engine.
It is still another object of the invention to provide a control
system for an engine having an air intake passage which can
effectively supply a reference heating electric current to a
temperature sensitive element, attain a highly accurate intake air
flow measurement signal, effectively improve the accuracy of
controlling the engine, and effectively remove noise signal
components to execute a highly accurate intake air flow
measurement.
According to an aspect of the present invention, there is provided
a control system for an engine having an air intake passage which
generates a signal corresponding to the operating state of the
engine and hence a control pulse signal corresponding to the speed
of the engine, and which controls the rise of a heating electric
current supplied to a temperature sensitive element set in the
intake manifold in response to the control pulse signal. The
heating electric current is continuously supplied to the element
until the temperature of the element reaches a certain specific
temperature where the predetermined difference between it's
temperature and the temperature of the air in the intake manifold
is obtained, once this occurs, it interrupts the current supplied
to the element.
Therefore, the length of time that the heating electric current is
supplied to the temperature sensitive element determines the heat
dissipating characteristic of the element, and the lengh of time
determines the air intake flow in the intake manifold. In this
case, the length of time that the heating electric current is
supplied is used as a measurement output signal represented in a
digital manner to be counted by a counter, this measurement output
signal is directly supplied to an engine control unit composed of a
microcomputer without using means for A/D conversion, and the unit
can be used for controlling the engine with a highly accurate
measurement signal.
Particularly, the measurement output signal, obtained by the
above-described means is generated in correspondence to the speed
of the engine, and in response to the timing of the fuel injection
to the engine and the amount of fuel injected, thereby effectively
controlling the operation of the engine.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view for describing the construction of a control
system for an engine having an air intake passage of a first
embodiment according to the present invention;
FIGS. 2 and 3 are views showing examples of the constructions of
temperature sensitive elements used in the construction of an
amount-of-intake air flow measuring means used in the above
embodiment;
FIG. 4 is a circuit diagram for describing the measuring means;
FIGS. 5A to 5D are waveform diagrams for describing the operation
states of the measuring means;
FIGS. 6 and 7 are graphical diagrams respectively showing the
relationship between the number of rotations of the engine and the
amount of air, and between the length of the pulse of a measurement
output signal and the amount of air;
FIGS. 8 and 9 are views respectively showing the constructions of
the second and third examples of the measuring means;
FIG. 10 is a view of the construction for describing the fourth
example of the measuring means to explain first pulse signal
generating means;
FIGS. 11 and 12 are flowcharts describing the operating states of
the pulse signal generating means;
FIG. 13 is a circuit diagram for describing the fifth example of
the measuring means;
FIG. 14 is a circuit diagram showing an example of a constant
current circuit used in the measuring means;
FIG. 15 is a circuit diagram showing the fifth example of the
measuring means;
FIG. 16 is a view showing an open collector buffer circuit used in
the measuring means;
FIGS. 17A to 17C are signal waveform diagrams for describing the
operation of the above-described examples;
FIGS. 18 and 19 are views showing examples of a tri state buffer
circuit;
FIGS. 20A to 20D are waveform diagrams describing the vibration
noise contained in a signal generated from the measuring means;
FIGS. 21A and 21B are waveform diagrams describing the states of
vibration noise;
FIG. 22 is a circuit diagram for describing the seventh example for
removing the noise;
FIGS. 23A and 23B are signal waveform diagrams for describing the
operation of the above examples; and
FIG. 24 is a circuit diagram for describing other methods for
removing the noise.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in more detail with
reference to the accompanying drawings.
FIG. 1 shows a control system of an engine 11 for electronically
controlling the amount of fuel injected in accordance with the
operating state of the engine. Air to the engine 11 is sucked
through an air intake manifold 13, from an air filter 12, to the
engine 11. The amount of air is controlled by a throttle valve 15
driven and controlled by an accelerator pedal 14. A temperature
sensitive element 17 which is part of a heat type air measuring
device 16 is set in the manifold 13. The element 17 is composed of
a heater made of platinum wire having temperature characteristics
controlled for generating heat by an electric current and varying
in its resistance value in accordance with the temperature. A
measurement output signal from the measuring device 16 is supplied
to an engine control unit 18 which includes a microcomputer. The
heating electric current of the element 17 is controlled by a
command from the control unit 18.
An output signal from a rotating speed sensor 19 for detecting the
speed of the engine 11, and, not shown in FIG. 1, a coolant
temperature detection signal, exhaust gas temperature detection
signal, and an air-to-fuel ratio detection signal of the engine 11
are also supplied to control unit 18 as the operating state
detection signals of the engine 11. The amount of fuel injected for
the operating state of the engine 11 at that time is calculated on
the basis of these detection signals, and supplied as a fuel
injection time setting signal to fuel injectors 201, 202, . . . set
in the cylinders of the engine 11.
In this case, signals for respectively setting the amounts of fuel
supplied to the injectors 201, 202, . . . are formed in
pulse-shaped signals set in a schedule. Data corresponding to the
lengths of time of the signals are temporarily stored and set in
the respective registers 211, 212, . . . to be stabilized to
control the opening of the injectors in the range of the length of
time, thereby controlling the amount of fuel injected in accordance
to the length of time.
The rotating speed sensor 19 has cams 191, 192 coaxially driven
rotatably with the engine 11, and a rotating angle detecting rotary
plate 193 having a number of teeth, electromagnetic pickups 194 to
196 set opposite and corresponding to the cams 191, 192 and the
plate 193 so that an angle signal corresponding to the specified
rotating angle of the engine 11 and pulse-shaped signals for
detecting and counting the further specified rotating angle
positions are picked up from the pickups 194 to 196.
Fuel collected from a fuel tank 23 by a fuel pump 22 is distributed
through a distributor 24 to the unit injectors 201, 202, . . . set
to the cylinders of the engine 11. Here, the pressure of the fuel
supplied to the distributor 24 is controlled in a constant state by
a pressure regulator 25, and the amount of fuel injected is
accurately controlled by the length of time the injector is
open.
The engine control unit 18 also applies a command to an igniter 26,
distributes ignition signals through a distributor 27 to ignition
coils 281, 282, . . . respectively provided at the cylinders of the
engine 11, and executes the control of the ignition timing adapted
for the operation of the engine 11.
FIG. 2 shows the temperature sensitive element 17 used in the
measuring device 16 employed in the control system for the engine
described above. A platinum resistance wire 172 is wound as a
resistance wire, having temperature characteristics, onto a ceramic
bobbin 171. Shafts 173, 174 made of a good conductive material are
projected as supporting shafts from both ends of the bobbin 171 to
connect both ends of the wire 172 to the shafts 173, 174. The
shafts 173, 174 are respectively supported by pins 175, 176 made of
a conductive material, and a heating electric current is supplied
through the wire 172 to the pins 175, 176. The wire 172 of the
element 17 thus constructed is set to be exposed to the air flow in
the manifold 13.
FIG. 3 shows another example of the element 17. A resistance wire
172, which is to become a heat generator, is formed by a printed
circuit on a membrane 177 made of an insulator. The membrane 177 is
supported by a supporting substrate 178 made of an insulator,
wiring circuits 179a, 179b to be connected to the wire 172 are
printed on the substrate 178, and a heating electric current is
supplied through the circuits to the wire 172.
FIG. 4 shows a circuit diagram of the measuring device 16 used as
described above. A temperature sensitive element 17 is fixedly set
as a heater in an air intake manifold 13, and a sub temperature
sensitive element 30 is also fixed upstream of the element 17 in
the manifold 13. The element 30 is composed of a resistance wire
(such as a platinum wire) in the same manner as the above-described
element 17. The resistance value is set corresponding to the
temperature of air passing through the manifold 13, and the wire is
used as an air temperature measuring means. Fixed resistors 31 and
32 are respectively connected to the elements 17 and 30, and a
bridge circuit is composed of the resistors 31, 32 and the elements
17, 30.
Connecting points a and b are for connecting the elements 17 and 30
to the resistors 31 and 32 respectively as the output terminal of
this bridge circuit and are connected to the input terminal of a
comparator 33, which detects the varying temperature of the element
17. In other words, a heating electric current is supplied to the
element 17, and when its temperature rises to the point where the
difference between its temperature and that of the air is the same
as the predetermined specified temperature difference (detected by
the element 30), an output signal from the comparator 33 rises.
The output signal from the comparator 33 is supplied as a reset
command signal to a flip-flop 34. This flip-flop 34 is controlled
to be set by a first pulse signal generated with every rotation of
the engine 11, and the flip-flop 34 is maintained in the set state
during a period from the first pulse signal to a second pulse
signal corresponding to the output from the comparator 33.
The output signal generated from the comparator 33 when the
flip-flop 34 is in the set state is produced as an output signal
through a buffer amplifier 35, and supplied to the base electrode
of a transistor 36, which controls an electric current supplied to
the bridge circuit which includes the elements 17 and 30. In other
words, when the flip-flop 34 is in the set state, the heating
electric current is supplied to the element 17. In this case, the
voltage value of the current supplied to the element 17 is set as a
reference.
The first pulse signal as shown in FIG. 5A is generated, for
example, with every rotation of the engine 11 corresponding to the
specified rotating angle of the engine 11. The flip-flop 34 is set
by the first pulse signal, and the output signal of the flip-flop
34 rises as shown in FIG. 5B, the transistor 36 is controlled to be
in the ON state by the output signal, and the current is supplied
to the element 17. In other words, the temperature of the element
17 is gradually raised as shown in FIG. 5C after the flip-flop 34
is inverted to the set state and the current is raised. The
temperature rising velocity of the element 17 is determined by the
heat dissipating effect corresponding to the air flow velocity
acted on the element 17.
When the temperature of the element 17 rises, so does its
resistance value. When the potential at a point a of this bridge
circuit falls to the state lower than the potential of a point b,
the output signal from the comparator 33 rises as a second pulse
signal as shown in FIG. 5D, thereby resetting the flip-flop 34.
More specifically, when the heating electric current, set to the
reference, is supplied to the element 17, the temperature of the
element 17 rises at a velocity corresponding to the amount of air
flowing in the manifold 13, and the length of time from the set of
the flip-flop 34 to the reset of the flip-flop 34 becomes
proportional to the amount of air flow.
In other words, the length of time of a period that the flip-flop
34 is set becomes a function of the intake air flow, the length of
time of the pulse-shaped signal generated from the set of the
flip-flop 34 to the reset of the flip-flop 34 becomes an air flow
measurement signal, which is produced as an output signal of the
measuring device and supplied to the engine control unit 18.
In the measuring device as described above, the element 17 is
controlled to be heated by the time length signal. Therefore, the
varying state of the output signal to the variation in the amount
of air flow can be increased as compared with the case that the
heating electric current is continuously supplied and set. Since
the state of the output signal is a pulse-shaped signal format and
the measured value is represented by the length of time, the output
signal can be simply converted to digital data by counting the
clock pulses. Further, the output signal, which is set by the
length of time and the amount of air flow, is generated in a period
corresponding to one rotation of the engine 11. In other words, the
air flow measurement signal used to calculate the amount of fuel to
be supplied to the engine is generated with every rotation of the
engine 11. Therefore, the control of calculating the amount of fuel
to be injected can be executed, so that it most closely matches the
operating state of the engine 11.
When the operating range of the engine 11 is observed in a
relationship between the number of rotations N of the engine 11 and
the amount of air flow, it becomes as shown in FIG. 6. In FIG. 6,
reference character a designates an idling state, reference
character b designates an idling full load state, reference
character c designates the maximum number of rotations in a full
load state, and reference character d designates the maximum number
of rotations in a racing state. The interior A of a quadrangle
designated by the a to d is the acutally usable range of the
engine, and the outsides B and C of the quadrangle are meaningless
in the ordinary usable range.
FIG. 7 shows the relationship between the length of time o, the
output pulse signal of the measuring device 16 and the actual
amount of air flow. The points a to d and the ranges A to C
correspond to those in FIG. 6. The unnecessary ranges B and C are
those in which the powers of the engine are large and small, and
critical values cannot be measured in these ranges, but a wide
range of air flows can be measured. Even when the output signal is
converted into digital data, the resolution is deteriorated only
extremely rarely in the high rotation low load range designated by
d, which is of no problem since this point is not required
particularly for the measuring control accuracy.
When the output signal of such a pulse state is attained, the
integrated value of one pulse period of the signal is outputted.
When considering this point, the measurement output signal is
generated in the state corresponding to the rotating state of the
engine. Therefore, the influence of the air intake pulsation caused
by the opening and closing of the engine intake valves can be
remarkably reduced.
In the embodiment described above, the measuring operation is
executed in a period corresponding to the rotating state of the
engine 11. However, this may correspond to the operating state of
the engine 22. For example, the measuring period may be set
corresponding to the injection timing of fuel which is controlled
in relation to the engine rotation. When thus set, the average
measuring output in the injection range can be attained even when
the injection period is altered, and the amount-of-air flow
measuring operation can be executed in the state adapted for the
operating state of the engine.
FIG. 8 shows the second example of the measuring device 16. This
device is constructed so that an output signal from a comparator 33
is supplied to a 1-chip microcomputer 40. A first pulse signal
corresponding to the operating state of the engine is supplied to
the microcomputer 40, and a constant-voltage circuit which has a
transistor 36, a differential amplifier 38 and a reference power
source 37 is controlled by the microcomputer 40.
More particularly, the signal inputted from the comparator 33 to
the microcomputer 40 is as shown in FIG. 5D, and the microcomputer
40 measures the interval between the input signal from the
comparator 33 and the first pulse signal. Then, the length of time
corresponding to the length of the pulse of the pulse-shaped signal
as shown in FIG. 5B is measured, for example, by means for
measuring a clock pulse.
Therefore, the output signal from the microcomputer 40 is not the
pulse signal controlled in the length of the pulse as shown, in
FIG. 4, but is produced as data converted from a serial data to
binary data, and transmitted to the engine control unit 18. Or, it
may be converted to a signal such as the air flow data, or the
fundamental amount of fuel injection data by calculating in the
microcomputer 40 and processing a table lookup.
The element 17 used in the above-described example is constructed
as a heat generating element having temperature-resistance
characteristics by itself. However, the element 17 may be composed
in combination with a heat generating element 171 for generating
heat by the heating electric current as shown, in FIG. 9 and a heat
sensitive resistance element 172 having temperature-resistance
characteristics, which may be constructed so that both are set in
such a manner that the element 172 is controlled to be heated by
the element 171.
When the amount of intaken air flowing in the manifold 13 is
measured by means shown in FIGS. 4 and 8, it has been described
that the rise of the heating electric current to the element 17 was
controlled in accordance with the first pulse signal generated at a
period corresponding to one rotation of the engine and the period
of measuring the amount of air flow was set. However, as the engine
11 varies its rotating speed between 500 to 10000 rpm, the
measuring period varies very largely with respect to the variation
in the rotating speed of the engine, so that it becomes difficult
to execute a stable air flow measuring operation at all times.
Further, when the measuring period is extremely short, it is
difficult to maintain resolution and measuring accuracy.
FIG. 10 shows the construction of a first pulse signal generation
controller for setting the measuring period by considering the
above-described points. In other words, a rotating speed signal N
generated at every rotation of the engine 11 is supplied to a
number-of-rotation discriminator 41. This discriminator 41 sets
therein a reference value N0 of the number of rotations of the
engine, discriminates the first state of "N>N0" and the second
state of "N<N0" by comparing the detected number of rotations N
with the reference value N0, and outputs it. When the
discrimination output of the first state is generated from the
discriminator 41, the discriminator 41 applies a command to a first
pulse cycle setter 42 to divide the number of rotations N of the
engine, in frequency, and to generate a period signal corresponding
to the signal attained as the result. Then, the discriminator
allows a pulse signal generator to generate a first pulse signal
corresponding to the period divided in frequency from the rotation
signal N.
When the discriminator 41 discriminates the second state, the
discriminator 41 applies a command to a second pulse cycle setter
44. The setter 44 generates a period signal corresponding to the
period of the rotation signal N, and allows the pulse signal
generator 44 to generate the first pulse signal of the period
corresponding to the number of rotations N of the engine.
More particularly, when the number of rotations N of the engine 11
is in a state lower than the set reference number of rotations N0,
the pulse signal generator 43 generates the first pulse signal
corresponding to the rotating period of the engine 11, thereby
executing the measuring operation for controlling the supply of the
heating electric current to the temperature sensitive elements.
When the rotating speed of the engine 11 rises so that the period
of the number-of-rotation detection signal becomes short, the
signal N is divided in frequency to be converted into a signal
having a long period, and the generator 43 generates the first
pulse signal corresponding to the period of the converted
signal.
FIG. 11 shows a flowchart of the flow of the first pulse signal
generating control state for controlling the measuring operation
described above. In step 100, the state of a frequency dividing
flag Xh is first discriminated. When the flag Xh is judged as "0"
in step 100, the control flow is advanced to step 101. In step 101,
the number of rotations N of the engine 11 at that time is compared
with 4000 rotations to discriminate the state of the engine at that
time. When the number of rotations of the engine at that time is
judged to be smaller than 4000 rotations, the control flow is
finished as the frequency dividing flag Xh remains "0". When the
number of rotations N is judged to be equal to or larger than 4000
rotations, the control flow is advanced to step 102, the flag Xh is
converted to "1", and finished.
When the flag Xh is judged to be "1" in step 100, the control flow
is advanced to step 103 to discriminate in which state the number
of rotations N of the engine is with respect to 3000 rotations.
When the number of rotations N is judged to be smaller than 3000
rotations, the control flow is advanced to step 104, the flag Xh is
converted to "1", and finished. When the number of rotations N is
judged to be equal to or larger than 3000 rotations in step 103,
the flow is finished as it is.
FIG. 12 shows the process of generating the first pulse signal for
executing the measuring operation corresponding to the frequency
dividing flag Xh to first discriminate the state of the flag Xh in
step 200. In step 200, when the flag Xh is judged to be "0", the
control flow is advance to step 201, and the signal generated
corresponding to one rotation of the engine 11 is outputted as the
first pulse signal as it is. Thereafter, in step 201, a skip flag
Xs is set to "1" and finished.
When the flag Xh is judged to be "1" in step 200, the control flow
is advanced to step 203 to discriminate the state of the skip flag
Xs in step 203. When the flag Xs is judged to be "0" in step 203,
the control flow is advanced to step 201 as it is, the first pulse
signal corresponding to the rotating period of the engine 11 is
outputted, and the flag Xs is converted to "1" in the next step
201. When the flag Xs is "1", the signal generated corresponding to
one rotation of the engine 22 is skipped to eliminate the
generation of the pulse signal, and the flag Xs is converted to "0"
in the next step 204.
More specifically, the flag Xh is controlled to be set to
correspond with the number of rotations of the engine 11, and when
the flag Xh is "1", the flag Xs is controlled to be converted to
"1" and "0" every time the detected signal, corresponding to the
period of one rotation of the engine 11, is inputted. Then the
output signal, to become the first pulse signal when the flag Xs is
"0", is generated and the first pulse signal of the period divided
by 2 in frequency from the rotation signal N is generated.
In the embodiment described above, the number of rotations of the
engine is divided into high and low speed ranges, the period signal
generated corresponding to the rotation of the engine in the high
speed range is divided in frequency, and the first pulse signal for
executing the measuring operation is set. However, a special
relationship may be stored and set between the period signal N
corresponding to the rotations of the engine and the first pulse
signal period, the period stored on the basis of the number of
rotations N of the engine may be read out, and the first pulse
signal may be generated corresponding to the read out period.
FIG. 13 shows the fifth example of the measuring device employed in
the present invention, wherein the said reference numerals as in
the first example in FIG. 4 denote the same parts in the fifth
example. In this example, the connecting point of a temperature
sensitive element 17 to a resistance element 31 is connected
through a resistor 50 to a comparator 33, and the input terminal of
the comparator 33 is grounded through a constant-current circuit
51. In other words, the circuit 51 operates to determine the value
of the temperature control of the element 17.
The constant-current circuit 51 is connected to the output side of
the resistor 50 as shown in FIG. 14, and the output side of the
resistor 50 is grounded through a transistor 511 and a resistor
512. Further, the voltage from a reference voltage power source 37
for controlling the voltage state of a heating electric current
supplied to the element 17 in a constant voltage state is divided
via resistors 513 and 514 and detected, the divided reference
voltage is compared by a comparator 515 with the voltage of the
terminal of the resistor 512, i.e., the voltage corresponding to
the current value flowed to the resistor 50, and the transistor 511
is controlled by a transistor 516 controlled by the compared output
from the comparator 515. In other words, the reference power source
of the circuit 51 is composed to commonly have the reference power
source 37 for controlling the heating electric current at a
constant voltage.
In the measuring device described above, it is an important
condition to attain accurate measuring data to control the current
supplied to the element 17 at a constant voltage. Therefore, the
reference voltage power source 37 for executing the control of the
constant voltage is required to be extremely accurate.
Consequently, the device becomes very expensive.
However, in the embodiment described above, the constant-current
circuit 51 is provided in the state for determining the control of
the temperature of the element 17, and the reference voltage power
source 37 is commonly used as the reference power source of the
circuit 51. Then, output errors to the constant voltage control
circuit of the current and the constant-current circuit 51 due to
an error in the power source 37 can cancel each other.
In other words, even if the accuracy of the power source 37 is not
sufficient, the accuracy of the measured output signal generated
from the measuring device 16 can be sufficiently high.
In the measuring device 16 shown and described in the previous
examples, the first pulse signal for instructing the measuring
operation is generated corresponding to the signal for detecting
the rotating state of the engine, and supplied to the measuring
device 16. Therefore, a special signal line for coupling the first
pulse signal to the measuring device 16 is necessary, and a
terminal for inputting the pulse signal is also required.
However, since the measuring device 17 is always mounted in an
environment in which a number of noises normally exist, i.e., in
the engine room of an automobile, it is restricted in the
disposition of the signal wires for instructing the measuring
operation.
FIG. 15 shows an example constructed by considering the
above-described points. When an output signal from a flip-flop 34
is produced as a measuring output through a buffer amplifier 35,
the signal is outputted through a terminal 61 of an open collector
buffer circuit 60, and supplied to the engine control unit.
Further, the terminal 61 is also used as an input terminal of the
first pulse signal to the measuring device 16, the first pulse
signal is supplied through an open collector buffer circuit 62 to
the terminal 61, and supplied as a set command signal to a
flip-flop 34. In the circuit in FIG. 15, the input/output is
executed in a negative logic.
FIG. 16 shows a detailed circuit example of the buffer circuit 60.
When the output is at a high level, the circuit 60 is constructed
to have high impedance. The buffer circuit 62, to which the first
pulse signal is supplied is also constructed with a circuit shown
in FIG. 16.
In the measuring device shown in FIG. 15, the first pulse signal
generated in the state corresponding to the rotation of the engine
is inputted through the buffer circuit 62 to the terminal 61 to set
the flip-flop 34. Then, the amount of air flowing in the intake
manifold is measured in the same manner as the case described with
reference to FIGS. 5A to 5D.
An output signal from the flip-flop 34 is supplied to the terminal
61 upon the inputting of the above-described first pulse signal,
and the measuring output signal corresponding to the setting and
resetting operations of the flip-flop 34 is produced through the
buffer circuit 60. The flip-flop 34 is set when the output signal
rises. Therefore, even when the output signal is supplied from the
set command input to the flip-flop 34, it does not affect the
operation of the measuring device.
The operating state of the example described above will be further
described. Assume that the first pulse signal supplied to the
buffer circuit 62 is in the state as shown in FIG. 17A, the
flip-flop 34 is controlled to be set or reset in the states as
shown in FIG. 17B, and the signal for controlling a transistor 36
is as shown in FIG. 17C.
In the embodiment described above, the buffer circuits 60 and 62
have been described as open collector types. However, these buffer
circuits may also be constructed as a tri-state type.
FIG. 18 shows a tri-state circuit used as a buffer circuit 60. An
input signal is supplied to an input terminal 601, and a control
signal is supplied to a control terminal 602. Then, transistors 603
and 604 are reciprocally controlled corresponding to the level
state of the control signal.
In other words, when the control signal is at a high level, the
input signal is inverted to be presented at an output terminal 605.
When the control signal is at a low level, the output terminal 605
has a high impedance.
When this circuit is applied to the device shown in FIG. 15, the
input terminal 601 is connected to the terminal 602, and used as an
input terminal.
FIG. 19 shows a tri-state circuit used as a buffer circuit 62. When
a control signal to the control terminal 602 is at a low level, a
signal coupled to the input terminal 601 is transmitted to the
output terminal 605 as it is. When the control signal is at a high
level, the output terminal 605 has a high impedance.
The embodiments described above will be further considered. Assume
that the first pulse signal for controlling the flip-flop 34 is
generated in the state shown in FIG. 20A, the flip-flop 34 is set
by the signal to control a transistor 36, and a pulse-shaped
heating electric current corresponding to the element 17 is
generated as shown in FIG. 20B. In this case, the state of the
current flowing to the element 17 and the resistance element 31
vibrates as shown in FIG. 20C by the distributed capacitance and
the inductance on the wires for controlling and transmitting the
current. The potential at the point of an input signal to the
comparator 33 of the connecting point to the element 17 and the
element 31 is proportional to that shown in FIG. 20C. Therefore,
the input potential to the comparator 33 with the potential of the
connecting point of the element 30 to the resistance element 33 as
a reference also vibrates as shown in FIG. 20D. Further, the time
constants for raising the potential at both input points of the
comparator 33 from the difference of the impedances become
different.
The varying length V1 of the waveform of FIG. 20D is a mere several
mV according to the operating conditions, and when the peak value
of the vibration of the waveform exceeds V1 so that the margin
length V2 becomes zero, the comparator 33 judges that the
temperature of the element 17 has reached the set temperature and
interrupts the current and is therefore in error.
In order to effectively eliminate the occurrence of the
above-described problem, the flip-flop 34 is constructed as a level
trigger type, in such a manner that, in the state that an input
signal exists in the set terminal, the flip-flop remains set even
when a reset command signal is supplied to the resetting terminal
of the flip-flop. Then, the length T1 of time to obtain an
effective polarity of the first pulse signal, used for controlling
the current, is set to a value larger than that of vibrating the
current as shown in FIG. 21A.
In other words, the flip-flop 34 remains set irrespective of the
output state of the comparator 33 during the length T1 of time, and
the flip-flop 34 is controlled by the output of the comparator 33
in the period T2, the state for proving the output of the
comparator 33. This means that the output of the comparator 33 is
masked during the length T1 of time of the first pulse signal, and
the air flow measuring operation is stably executed.
The first pulse signal having a predetermined pulse length may be
set in this manner, but the pulse length T1 is set as it is to the
lower limit value of the measuring output. Therefore, the length of
the first pulse signal is desired to be as short as possible.
However, a difficulty which might sometimes occur with using the
first pulse signal having a short length T1 of time according to
the environmental conditions such as the wire state used or the
noise presenting state. The load to the heating signal generator
increases.
FIG. 22 shows an example of means for generating the first pulse
signal for controlling the heating of an electric current and
considers the above-described points. An edge trigger type
monostable multivibrator 66 is constructed to control the rise of
the inputted first pulse signal at the edge, and the flip-flop 34
is controlled by the output signal set in the length of the pulse
from the multivibrator 66.
In other words, when the first pulse signal as shown in FIG. 23A is
generated, the output signal of the multivibrator 66 rises
corresponding to the rising edge of the signal as shown in FIG.
23B, and the flip-flop 34 remains set during the length T1 of time
set by a resistor 661 and a capacitor 662 for setting the time
constant of the multivibrator 66.
FIG. 24 shows still another example of signal generating means for
controlling the heating of an electric current. A switch circuit 67
is provided between a comparator 33 and a flip-flop 34, which is of
an edge trigger type.
In this case, the switch circuit 67 may be composed of a digital
switch circuit having in combination an analog switch and a logic
circuit.
More specifically, in this circuit, the output of the comparator 33
is not transmitted to the flip-flop 34 for a predetermined period
of time by the output signal of the multivibrator 66, and the
masking operation is executed during the length T1 of time in the
same manner as described above.
In addition, when the flip-flop 34 is composed of an edge trigger
type with a preset terminal, the output of the multivibrator 66 may
be supplied to the preset terminal of the flip-flop 34.
The present invention having been described may be modified so that
the temperature sensitive element used as the heater is supplied
with a constant current in place of a constant voltage.
* * * * *